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Aquatic surveys and re-assessment of sites within the Middle Powder River Watershed

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Aquatic surveys and re-assessment of sites within the Middle Powder River Watershed


Published 2012
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Includes bibliographical references (pages 18-19)

Introduction -- Powder River Study Sites -- Methods -- Habitat and Water Quality Collection and Analysis -- Fish Collection and Analysis -- Macroinvertebrate Collection and Analysis -- Results and Discussion -- Habitat and Water Quality Results and Analysis -- Fish Community Results and Analysis -- Macroinvertebrate Community Analysis -- Conclusions and Recommendations -- Literature Cited -- Appendix A: Global/State Rank Definitions -- Appendix B: Raw fish data and IBI metric calculation from Powder River sites -- Appendix C: Macroinvertebrate taxa lists, abundance and plains MMI calculations at each site

The project goals of the 2011 Aquatic Surveys and Assessment of the Middle Powder Watershed were to: 1) revisit five integrator sites established and sampled in 2005 to assess aquatic community changes during this time period; 2) perform habitat-targeted surveys for the rare sand-dwelling mayfly community; and 3) interpret key community and watershed indicators (against reference condition standards) to determine aquatic condition status and trends since the development of coalbed natural gas (CBNG) wells in the watershed. Inventory work occurred on BLM lands where possible to enable informed management at the local site scale. Fish and macroinvertebrate samples were collected at six mainstem Powder River sites in MT (Moorhead Bridge site added in 2011) for this BLM assessment. Fish Communities: Fish surveys were performed at each site using the 300 m seining protocols developed by Bramblett et al. (2005) for MT Fish, Wildlife and Parks. Overall, we captured 374 individuals and identified eight native species at the six mainstem Powder River sites. Despite using the same effort during similar river flows, fish numbers and diversity were significantly lower (~1/4 as many individuals) in 2011 than in 2005, which recorded 1299 individuals of 13 fish species. Native fish species averaged six per site in 2011, whereas in 2005, sites averaged seven per site (7.5 species is Expected {E} at reference condition). Flathead chubs were the dominant members of this river sections fish community in 2011 averaging 66% of the individuals collected, while in 2005 they only made up ~28% with sand shiners dominating the catch (60%). The exotic carp and introduced plains killifish were not collected at any of the 2011 sites where they were reported in 2005. The Sturgeon Chub, a MT species of concern previously common in this reach, was not collected in 2011 and only at one downstream site in 2005, indicating a sustained decline or absence in this reach. Fish communities across all sites scored relatively lower with the IBI and Observed vs. Expected (O/E) in 2011 than in 2005 (averaging 54.8 vs. 58.4 and 0.8 vs. 0.9, respectively), but these differences were not significant (FTEST, p= 0.25 and 0.74). The Moorhead Bridge site was the exception for 2011 with increased IBI and O/E scores. When calculating O/E values, four of the six sites scored within the 1.2-0.8 unimpaired/good integrity threshold, while sites POW3 and POW6 ranked impaired with scores of 0.57 and 0.63. The fish community scores did not correlate with the macroinvertebrate DEQ MMI or O/E scores (r=0.09 and 0.07), but did have a positive relationship with the BLM Habitat Scores (r=0.51 and 0.55). Macroinvertebrate Communities: Paired EMAP-protocol macroinvertebrate samples were collected at each site replicating efforts from 2005. Overall, 64 total taxa were reported from the sites in 2011, an increase from 59 taxa in 2005. Average macroinvertebrate-taxa richness per site was 28 taxa, which is a significant increase from 23.4 taxa per site reported in 2005 (p <0.03). All EMAP samples agreed in ranking the six Powder River sites non-impaired with DEQ MMI plains-index scores>37 and the O/E, but the O/E scores based on species expected only>50% of the time report all sites significantly below the impairment threshold. Reach-Wide EMAP samples collected two of the five species of rare sand-dwelling mayflies, Homoeoneuria alleni and Anepeorus rusticus not sampled with the Targeted-Riffle Protocols. Targeted sampling of the rare sand-dwelling mayfly community with the over-sized dip net proved laborious and ineffective at increasing occurrence records or estimating densities. There were no discernible trends in the MMI or O/E index scores from the Wyoming Border to Broadus, and MMI scores were not significantly different than 2005 scores. However, the occurrence and abundance of some sensitive/Species of Concern (SOC) mayfly species has significantly decreased from the Wyoming Border to Moorhead Bridge from 2005 to 2011, while the abundance of the stonefly, Acroneuria abnormis has significantly increased across the study area in recent years. Community Integrity: Multiple lines of evidence (fish and macroinvertebrates) indicate a continued decline in the biological integrity of this reach of the Powder River. This is particularly noted in fish and SOC mayfly species declines between the Wyoming border and Moorhead Bridge. From a long-term perspective, the fish community at the WY border looks significantly different than it did 30 years ago, as it continues to lose sensitive species and biological integrity. Concurrent studies have found that the maximum concentrations of alkalinity in the Powder River also occurred in this reach (Petersen et al. 2011) potentially implicating cumulative effects from coalbed natural gas extraction-related outflows from upstream in Wyoming as likely contributors to this biological condition. Community Integrity results from the 2011 fish and macroinvertebrate surveys combined to rank the Powder River reach at the Moorhead Bridge Site as the most biologically intact, followed by Powder River Site #5 upstream of Rough Creek (POW#5). In 2005, the Powder River reach at the Wyoming border (POW#1) and POW#5 had the highest fish biotic integrity (IBI). Powder River Site #5 was also the only site where we collected Sturgeon Chubs (MT SOC) in 2005, but we failed to collect any during the 2011 sampling

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Volume 2012
Publisher Helena, Montana : Montana Natural heritage Program
Year 2012
Pages 52
Language English
Book contributor Montana State Library
Contributor usage rights See terms
Collection MontanaStateLibrary

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